While conventional photography records a two-dimensional projection of the intensity profile of an object onto a fixed plane, holography records enough information to enable recreation of the three-dimensional optical field emanating from an object, including both the amplitude and phase of the optical field. The three-dimensional recording is made possible by the interference of the object's optical field with a so-called reference field and therefore requires coherence between the two fields. In the original conception of holography, the reference was realized from a part of the illumination undisturbed by the object. The invention of the laser made it possible to provide the coherent reference field explicitly and with a high degree of freedom in the optical configurations. Three-dimensional holographic images quickly captured the imagination of the general public and lead to a multitude of new technological applications. In such applications, coherence of the reference light was at the core of the holographic principle. Unfortunately, this has been a major impediment to a wider range of applications of holography because it requires special illumination sources, such as lasers, or significantly constraining the optical configurations.
Digital holography is an emergent imaging technology that has been made possible by advances in computing and image sensor technologies. Whereas photography is made faster and more convenient by the digital technologies, the digital implementation of holography has a more fundamental impact in new imaging modalities that have been impossible or impractical in analog versions. Once a hologram is acquired and stored in a computer as an array of complex numbers that represent the amplitude and phase of the optical fields, the hologram can be numerically manipulated in highly flexible and versatile manners.
While digital holography has been used in various scientific contexts, it has not been implemented to capture color images of scenes illuminated by incoherent light. If the requirement of coherent illumination can be removed, it would open doors to a wide range of new applications, including holography of scenes illuminated with ordinary light sources such as day light, room light, LEDs, etc. Holographic imaging could be effectively applied to all areas of common photography. Many areas of scientific imaging, from fluorescence microscopy to astronomical telescopy, that have been inaccessible to holography because of coherent illumination requirement, can now benefit from many powerful and versatile holographic imaging and processing techniques.